Symmetrical, spherical or nearly spherical containers are known, which according to their use may be formed from a skin of supple and resistant material, such as the envelope used in airships, or from a shell of rigid and resistant material, as in spherical tanks used for containing gases under pressure or gases of which the liquid phase cannot be maintained in equilibrium except under pressure.
In the case of an airship, and more particularly a pressurized balloon, i.e. a ballon of which the closed envelope is sufficiently resistant to accept a certain pressure, and which, consequently, its volume remaining constant, is capable of flying for several months at a steady level, the best possible ratio between the resistance and weight of the envelope and equally the best possible air-tightness is sought. Until the present time, these aims were achieved by a spherical balloon made of polyester film.
In the case of tanks designed to contain a gas under pressure or a gas in isobaric equilibrium with its liquid, the spherical shape is chosen in order to allow a uniform distribution of the stresses in the shell and a minimum shell weight. Although this latter parameter is not generally of fundamental importance, it is desirable with regard to spatial applications, for example, to achieve the same aims as in balloon envelopes. For ordinary applications, the reduction in weight and thus of the material used, is not to be neglected. In addition, ease of construction is sought and the use of easily weldable materials greatly contributes here.
The invention has attempted to resolve these difficulties by combining an optimal distribution of the forces in the skin of a container under pressure and a renewal of the stresses exercised by the pressure force, by a particular structure.